This invention relates to coating and adhesive compositions based upon novel monohydroxylated diene polymers. More specifically, the invention relates to polyurethane compositions containing monohydroxylated polydiene block copolymers or random copolymers of at least two different monomers, at least one of which is a diene.
Monohydroxylated polydienes are known. Most of these polymers are homopolymers of one diene or another. For example, monohydroxlated polybutadienes are known in the art for use in some kinds of coating formulations. U.S. Pat. No. 4,242,468 describes solventless polyurethane coatings having improved flexibility resulting from incorporation of monohydroxylated polybutadienes. Epoxidized versions of hydroxylated polybutadienes are known as well. Low viscosity epoxidized polydiene polymers are also known for use in coatings. Such polymers are described in commonly assigned U.S. Pat. Nos. 5,229,464 and 5,247,026.
The reaction of diisocyanate, or polyisocyanate curing agents with polyol resins, such as alkyd resins, polyester resins, epoxy resins or acrylic resins having hydroxyl groups, is widely used to make coatings and adhesives for substrates like metals, wood and plastics. In conventional coatings, high molecular weight components could be used in solvent solution that make coatings having a broad range of properties. However, solventless or low solvent coatings, which have been developed in response to environmental problems with solvents, must be formed from low molecular weight components which typically make hard coatings that have poor flexibility and poor adhesion to substrates.
The monohydroxylated polymers described above have certain disadvantages that make them unsuitable for use in polyurethane coatings. Their primary limitation is that they are too nonpolar and so do not give phase stable blends in the coating formulations. The key requirement appears to be that all of the components, the monohydroxylated polymer, the polyol resin, and the isocyanate curing agent, must be compatible.